Updating README.md to resolve license dating
Updating README.md to resolve license dating

Changed 2016 to 2017 to resolve any license dating issues.
piskelapp/piskel,juliandescottes/piskel,piskelapp/piskel,GMartigny/piskel,juliandescottes/piskel,piskelapp/piskel,juliandescottes/piskel,GMartigny/piskel,GMartigny/piskel